Red LocTite

Try red LocTite if the bar end is just slipping a bit. If the bar end still isn't stable, the old stand by, an aluminum can shim wrapped @ the bar w/red LocTite under the bar end. Beyond that, replace the bar with a Syntace or 3T bar.

If it's any consolation, I haven't had the best of luck w/Ritchey components over the years either.